With the widespread use of digital cameras, photographs have been frequently dealt with in the form of image data. With this trend, it has become common to enjoy photographs in the following two ways. The first one is the conventional way that people view developed photographs. The second one is the new way that people causes an image display device to display thereon photographs stored in the form of image data.
There area various kinds of display methods for displaying a plurality of photographs on an image display device. Among the methods, slideshow display and thumbnail list display are typical display methods in widespread use.
The slideshow display is a display method in which a plurality of photographs are displayed in succession while being changed at regular time intervals. Users can view the photographs displayed in succession with the passage of time as if they watch moving images. Meanwhile, the thumbnail list display is a display method in which thumbnails which are reduced images of a plurality of photographs are displayed at a time. The thumbnail list display is useful in selecting a desired image from among a plurality of images.
An image display device capable of displaying a plurality of photographs in slideshow format is, for example, a personal computer disclosed in Japanese Unexamined Patent Publication No. 326885/2001 (Tokukai 2001-326885; published on Jan. 22, 2001). The personal computer disclosed in the above-mentioned publication enhances convenience for a user by allowing the user to select photographs in thumbnail list display, thereafter performing slideshow display of the selected photographs and by returning to the thumbnail list display after the completion of the slideshow display.
Another image display device capable of performing slideshow display is a digital camera disclosed in Japanese Unexamined Patent Publication No. 184109/2005 (Tokukai 2005-184109; published on Jul. 7, 2005). The above-mentioned publication discloses the following technique: when the digital camera detects a deletion operation during slideshow display, the digital camera suspends the slideshow display, displays side by side on a monitor (a) an image displayed at a point in time when the deletion operation was detected and (b) an image displayed before the image (a), and detects a selection instruction, after which the digital camera returns to the slideshow display. This enhances convenience in deleting an image included in slideshow.
In addition, still another image display device is known. This image display device can display photographs which are stored in a server device located far from the image display device, through the use of a network such as the Internet. Example of such an image display device is disclosed in Japanese PCT National Phase Unexamined Patent Publication No. 506349/2004 (Tokuhyo 2004-506349; published on Feb. 26, 2004).
However, the image display device which performs slideshow display has the problem that a target image to be displayed cannot be displayed at a timing at which the target image is to be displayed. That is, the image display device has the problem that display delay can occur. The display delay causes the problem that the user keeps waiting until the target image to be displayed is displayed.
In the slideshow display, when the time comes to display a next image, the next image must be displayed immediately. Further, in response to a user's instruction to display an image (e.g. next or previous image) other than an image currently displayed during the slideshow display, it is preferable to display the image immediately. Thus, the slideshow display requires display of a target image to be displayed at a proper timing.
However, image data with a high volume of image information, such as photograph, is generally the one obtained by compressing original image information. That is, the image data must be expanded or decoded to display an image included in the image data. For this reason, when the processing is started after the time comes to display a target, there occurs display delay of at least the amount of time required for expansion of the image data.
The problem of display delay becomes more serious in an image display device which acquires image data to be displayed in slideshow from a server device far away from the image display device through a network to display the acquired image data. This is because there occurs display delay of not only the amount of time required for expansion of the image data but also the amount of time required for acquisition of the image data.
Considered as measures that can be taken to prevent the above-mentioned display delay are acquiring in advance image data to be displayed in slideshow display or expanding in advance image data to be displayed in slideshow display. However, in order to perform such processes, it is necessary to provide the image display device with a storage device for storing acquired image data and expanded image data. The larger data size of image data, and the larger the number of sets of image data included in slideshow, the higher a required storage capacity is. Therefore, in order to acquire in advance image data to be displayed in slideshow or to expand in advance image data to be displayed in slideshow, a high-capacity storage device needs to be provided. As a result, cost increase is inevitable.